Fatty change in the liver results from excessive accumulation of lipids within hepatocytes. Fatty liver is the accumulation of triglycerides and other fats in the liver cells. Fatty liver disease can range from fatty liver alone (simple fatty liver, steatosis) to fatty liver associated with hepatic inflammation (steatohepatitis). Although having fat in the liver is not normal, by itself it probably causes little harm or permanent damage. Steatosis is generally believed to be a benign condition, with rare progression to chronic liver disease. In contrast, steatohepatitis may progress to liver fibrosis and cirrhosis, can be associated with hepatocellular carcinoma and may result in liver-related morbidity and mortality.
Steatosis can occur with the use of alcohol (alcohol-related fatty liver) or in the absence of alcohol. Steatohepatitis may be related to alcohol-induced hepatic damage or may be unrelated to alcohol. If steatohepatitis is present but a history of alcohol use is not, the condition is termed nonalcoholic steatohepatitis (NASH).
In the absence of alcohol the main risk factors for simple fatty liver and NASH are obesity, diabetes, and high triglyceride levels. In NASH, fat builds up in the liver and eventually causes scar tissue. This type of hepatitis appears to be associated with diabetes, protein malnutrition, obesity, coronary artery disease, and treatment with corticosteroid medications. Fibrosis or cirrhosis in the liver is present in 15-50% of patients with NASH. Approximately 30% of patients with fibrosis develop cirrhosis after 10 years.
Fatty liver disease is now the most common cause for elevated liver function tests in the United States. It is now probably the leading reason for mild elevations of transaminases. Steatosis affects approximately 25-35% of the general population. Non-alcoholic fatty liver disease (including steatosis and steatohepatitis) (NAFLD) is found in over 80% of patients who are obese. NASH affects 2 to 5 percent of Americans and has been detected in 1.2-9% of patients undergoing routine liver biopsy. Over 50% of patients undergoing bariatric surgery have NASH. The disease strikes males and females; early studies report >70% of cases were in females but recent studies report 50% of patients are females. Fatty liver occurs in all age groups. In the United States NASH is the most common liver disease among adolescents and is the third most common cause of chronic liver disease in adults (after hepatitis C and alcohol).
Both NASH and NAFLD are becoming more common, possibly because of the greater number of Americans with obesity. In the past 10 years, the rate of obesity has doubled in adults and tripled in children. Obesity also contributes to diabetes and high blood cholesterol, which can further complicate the health of someone with NASH. Diabetes and high blood cholesterol are also becoming more common among Americans.
NASH is usually a silent disease with few or no symptoms. Patients generally feel well in the early stages and only begin to have symptoms—such as fatigue, weight loss, and weakness—once the disease is more advanced or cirrhosis develops. The progression of NASH can take years, even decades. The process can stop and, in some cases, reverse on its own without specific therapy. Or NASH can slowly worsen, causing scarring or “fibrosis” to appear and accumulate in the liver. As fibrosis worsens, cirrhosis develops; the liver becomes seriously scarred, hardened, and unable to function normally. Not every person with NASH develops cirrhosis, but once serious scarring or cirrhosis is present, few treatments can halt the progression. A person with cirrhosis experiences fluid retention, muscle wasting, bleeding from the intestines, and liver failure. Liver transplantation is the only treatment for advanced cirrhosis with liver failure, and transplantation is increasingly performed in people with NASH. NASH ranks as one of the major causes of cirrhosis in America, behind hepatitis C and alcoholic liver disease.
NASH is usually first suspected in a person who is found to have elevations in liver tests that are included in routine blood test panels, such as alanine aminotransferase (ALT) or aspartate aminotransferase (AST). When further evaluation shows no apparent reason for liver disease (such as medications, viral hepatitis, or excessive use of alcohol) and when x-rays or imaging studies of the liver show fat, NASH is suspected. The only means of proving a diagnosis of NASH and separating it from simple fatty liver is a liver biopsy. A liver biopsy requires a needle to be inserted through the skin and the removal of a small piece of the liver. If the tissue shows fat without inflammation and damage, simple fatty liver is diagnosed. NASH is diagnosed when microscopic examination of the tissue shows fat along with inflammation and damage to liver cells. A biopsy is required to determine whether scar tissue has developed in the liver. Currently, no blood tests or scans can reliably provide this information. Therefore there exists a need for a less invasive diagnostic method (i.e. a method that would not require a biopsy).